The present invention relates to a method and apparatus for measuring Raman signals by radiating a detection surface on which an analyte has been placed with excitation light and, in a state where an enhanced electric field has been generated at the detection surface, detecting Raman scattered light from the analyte.
Raman spectroscopy is a technique, used for identifying substances and other purposes, in which Raman scattered light obtained by radiating a substance with single-wavelength light is spectrally analyzed to give Raman scattered light signals. Raman spectroscopy can be used to measure (e.g., identify) biosamples.
In addition, as mentioned in the method for quantitatively analyzing a substrate by Raman spectroscopy described in JP 2000-258346 A, because there is a correlation between the concentration of the substance to be assayed and the intensity of the Raman scattered light, it is possible to determine the concentration or amount of an analyte based on the intensity of the Raman scattered light.
However, Raman scattered light obtained from the substance (i.e., the analyte) is weak, making it difficult to carry out such measurement at a high sensitivity.
To address this problem, JP 2005-172569 A discloses a method which uses a microstructure plate having formed thereon a detection surface where a plurality of fine metal particles of a size capable of exciting localized plasmons are disposed, which region, when irradiated with light, forms an enhanced electric field and amplifies Raman scattered light.
By employing surface-enhanced Raman scattering (SERS), which generates an enhanced electric field on the detection surface and thereby increases the signal intensity of Raman scattered light, it is possible to detect an analyte even when, owing to a low concentration, for example, little analyte is present on the detection surface.
U.S. Pat. No. 6,888,629, which relates to a method for detecting an analyte by the SERS technique, describes a method wherein signals other than Raman scattered light from the analyte (secondary signals) are filtered from all the signals detected so as to extract Raman scattered light signals representing the analyte. The secondary signals are data that have been stored in a processor, and detection is described as being carried out by detecting the Raman scattered light in a state where the analyte is not loaded in the measurement apparatus.